In the Universal Mobile Telecommunications System (UMTS) system, User Equipment (UE) and NodeBs (NBs) or base stations (BSs) communicate via a plurality of physical and logical channels. An Uplink High Speed-Dedicated Physical Control Channel (HS-DPCCH) carries to the NodeB acknowledgment information and current channel quality indicator (CQI) of the UE. This value is then used by the NodeB to calculate how much data to send to the UE during the next transmission, such as via a High-Speed Downlink Shared Channel (HS-DSCH) or other channel. The HS-DSCH is a transport channel shared among multiple users as a radio access bearer, and can be mapped onto one or several physical channels (also known as codes) according to a spreading factor.
In the UMTS system, a “standalone HS-DPCCH without ongoing E-DCH (Enhanced Dedicated Channel) transmission” capability has been added as a sub-feature of UMTS Release-11 “Further Enhancements for CELL_FACH” feature. This “standalone HS-DPCCH transmission” allows the UE to provide channel quality information (CQI) and downlink ACK/NACK information to improve the HS-DSCH transmission in CELL_FACH state without the presence of uplink traffic (in contrast to a UMTS Rel-8 solution where HS-DPCCH is opportunistically used in response to the UE's acquisition of common E-DCH to send uplink traffic).
This “HS-DPCCH without ongoing E-DCH transmission” is triggered at the UE by an HS-SCCH order from the NodeB prior to UE downlink HS-DSCH transmission. There is no ACK function in the uplink in response to the HS-SCCH order triggering the standalone HS-DPCCH, and as per 3GPP specification (25.308-11.5.0, section 23.1): “upon reception of an HS-SCCH order for HS-DPCCH without ongoing E-DCH transmission, if random access procedure fails and there is no uplink data in the UE buffer, the UE does not re-initiate the random access procedure unless another HS-SCCH order is received.”
When the HS-SCCH order fails to generate the common E-DCH acquisition (and by extension, the acquisition of HS-DPCCH) by the UE, the NodeB currently does not know the optimum time to resend the HS-SCCH order and whether to (a) continue the resending of HS-SCCH order until expiry of a Discard Timer (25.433, 9.2.1.24E) which operates to clear the HS-DSCH data queue; or (b) stop resending of HS-SCCH order and proceed with blind HS-DSCH transmission as in Rel-8. If approach (b) is taken, then the HS-DSCH transmission is not optimum because there's no DL ACK/NACK feedback until the UE acquires the common E-DCH to send RLC ACK in response to the downlink data.
One possible solution is for the NodeB to perform blind repetition of HS-SCCH order until HS-DPCCH acquisition is complete.
Unfortunately, to ensure reliability of HS-SCCH, high power has to be used and this would inject interference in the downlink, in addition to the waste of (HS-SCCH) code resource. Too short a blind repetition period would increase the interference and code waste, while too long a blind repetition period would add latency. In addition, since the NodeB does not have deep knowledge of individual UE QoS policies, it would need to treat all UEs the same (e.g. either all UEs would have the HS-SCCH order blindly repeated a finite number of times before blind HS-DSCH transmission would occur, or all UEs would have the HS-SCCH order blindly repeated indefinitely until traffic is discarded in the NodeB queue due to a discard timer).